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Organic field-effect transistors (OFETs) are considered almost purely interfacial devices with charge current mainly confined in the first two semiconducting layers in contact with the dielectric with no active role of the film thickness exceeding six to eight monolayers (MLs). By a combined electronic, morphological, structural, and theoretical investigation, it is demonstrated that the charge mobility and source-drain current in 2,20-(2,20-bithiophene-5,50-diyl)bis(5-butyl-5H-thieno[2,3-c]pyrrole-4,6)-dione (NT4N) organic transistors directly correlate with the out-of-plane domain size and crystallite orientation in the vertical direction, well beyond the dielectric interfacial layers. Polycrystalline films with thickness as high as 75 nm (approximate to 30 MLs) and 3D molecular architecture provide the best electrical and optoelectronic OFET characteristics, highlighting that the molecular orientational order in the bulk of the film is the key-enabling factor for optimum device performance. X-ray scattering analysis and multiscale simulations reveal the functional correlation between the thickness-dependent molecular packing, electron mobility, and vertical charge distribution. These results call for a broader view of the fundamental mechanisms that govern field-effect charge transport in OFETs beyond the interfacial 2D paradigm and demonstrate the unexpected role of the out-of-plane domain size and crystallite orientation in polycrystalline films to achieve optimum electronic and optoelectronic properties in organic transistors.

Electrolyte-Gated Organic Field-Effect Transistors (EGOFETs) offer many opportunities for the development of low-cost and low-power electronics suitable for applications like sensors and point-of-care tests; however, EGOFETs can be affected by the drift of their operative point that causes signals distortion and loss of information during sensing applications. Here, a blend of 2,8-Difluoro-5,11-bis(triethylsilylethynyl)anthradithiophene (diF-TES-ADT) and polystyrene (PS) is used as the active material for the fabrication of dual-gate EGOFETs. We exploited the dual-gate architecture to improve EGOFETs stability by implementing digital feedback that uses the back-gate electrode to compensate dynamically for the transistor threshold voltage allowing us to fix its operative point for prolonged tests (>10 h) with different aqueous solutions (Milli-Q water, NaCl 0.1 M and a physiological solution). The presented real-time threshold voltage compensation does not only allow to steady EGOFETs DC output current, but it also preserves EGOFETs sensing capability for the detection of signals with frequencies as low as 1 Hz., The research leading to these results has received funding from the University of Padua, Department of Chemical Sciences (Grants: P-DISC#09BIRD2019-UNIPD - SMOW -; P-DiSC#11NExuS_BIRD2020-UNIPD - CARBON-FET -). It is further funded by the Italian Ministry of Education, Universities and Research through the project entitled “Nanochemistry for Energy and Health, NExuS” (the national funding network termed “Dipartimenti di Eccellenza” awarded to the Department of Chemical Sciences at the University of Padua). This work was partially supported by the University of Padua, Department of Information Engineering, under the initiative Project PROACTIVE 2018, and by MIUR (Italian Minister for Education) under the initiative “Departments of Excellence” (Law 232/2016). This work was funded by the Spanish Ministry of Science and Innovation with the project GENESIS PID2019-111682RB-I00 and through the “Severo Ochoa” Programme for Centers of Excellence in R&D (FUNFUTURE CEX2019-000917-S), and the Generalitat de Catalunya (2017-SGR-918). S. R. acknowledges her FPI fellowship and is enrolled in the UAB PhD program., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).

We studied the hysteresis and electric field effects on planar CH3NH3PbI3 perovskite devices, synthetized from laser-ablated precursors, by means of electrical characterizations at different scan rates and optical measurements. The aim of our investigation is to characterize the phenomena behind perovskite degradation under prolonged applied electric field. Using a perovskite more resistant to electric field induced degradation, we run long time characterizations that were not accomplishable before. Thus, we distinguished all the degradation-involved phenomena. The results point to the presence of ions migrating in the perovskite when the device is biased. Our data showed that ion migration degrades the interfaces with the consequent creation of degradation layers that limit the current injected in the device and the extracted photocurrent. These layers where detected also by means of optical Raman characterization. In order to explain the details of the mechanisms concurring to the observed behaviors, we presented a qualitative model. The observed phenomena exacerbated by the planar structure are even more destructive on standard solution processed perovskites to which the results of this work can be extended. Since, the same degradation dynamics occur on vertical devices, typical on perovskite solar cells, this work provides a useful in-depth analysis of the ionic migration effects.

Electrolyte-gated organic field-effect transistors (EGOFETs) were fabricated using 6,13-Bis(triisopropylsilylethynyl)pentacene (TIPS-Pentacene) as a p-type organic semiconductor. The devices were characterized as reference-less (RL) EGOFETs, and the self-polarization mechanism was studied. The fact that EGOFETs can exhibit field-effect behavior even without the gate electrode was demonstrated. This work provides useful guidelines for optimizing RL-EGOFET technology.

We have studied the effects of an Electrostatic discharge stress on polymeric solar cells, employing P3HT:PCBM as active layer. All the analyzed devices featured a behavior strongly related to the evolution of the internal parasitic paths. We found that the degradation of the organic solar cells during the stress is related to the initial shunt condition. In addition, no breakdown occurred during the stress and only minor changes are visible from the photocurrent characteristics.

In this work, a new simple and easy to use technique for parameter extraction in thin film transistors is presented and discussed. To avoid the approximations needed to extract the parameters from the linear regime, our method operates in the saturation regime allowing for the correct determination of all the transistor parameters, including its parasitic resistances and the mobility enhancement factor. To prove the efficacy of the presented technique, we extrapolated the parameters from simulated transistors with increasing parasitic resistances, showing that the presented method allows a much better estimation of the transistors parameters with respect to standard extrapolation techniques. Finally, we experimentally validate our procedure by performing a complete characterization of both organic and inorganic transistors featuring dihexyl-quaterthiophene and indium-gallium-zinc-oxide as semiconducting materials, respectively.

In this work, we studied the impact of stair-case gate bias stress on flexible Indium-Gallium-Zinc-Oxide Thin-Film Transistors and we estimated the breakdown voltage for different channel aspect ratios. The results show that the breakdown voltage exhibits a remarkable dependence on the channel width, while exposing no or marginal dependence on the channel length. The analysis of the threshold voltage evolution shows that after an initial increase, a remarkable decrease occurs for larger bias, indicating the action of at least two charge trapping phenomena.

A general equivalent circuit model for the metal/organic semiconductor (OSC)/liquid/metal system is presented. Each circuital element, representative of a physically observable phenomenon associated with the device working principle, is analyzed and discussed. Two case studies of electrochemical impedance spectroscopy of devices featuring NaCl (concentration of 0.1 M) and MilliQ water as liquid are reported, showing that both cases can be considered as a particular case of the general model presented in this paper. Experimental verification of the two practical cases is achieved by performing measurements onto electrodes coated by either an n-type or a p-type OSC deposited by sublimation or drop casting, respectively. The good agreement with the experimental data makes our model a useful tool for the characterization and failure analysis of electronic devices, such as water-gated transistors, electrophysiological interfaces, fuel cells, and others electrochemical systems.

Electrolyte-gated organic field-effect transistors (EGOFETs) have been fabricated using 6,13-Bis (triisopropyl-silylethynyl) pentacene (TIPS-pentacene) as an organic semiconductor active material. Despite the organic semiconductor being deposited in air by drop casting, our EGOFETs showed performance comparable with state-of-the-art technologies, and devices kept their functionalities while gated with saline solution at 37 °C for several days. In addition, the biocompatibility of the material was successfully investigated, promoting the use of TIPS-pentacene -based EGOFETs for biosensing applications.

Organic field-effect transistors (OFETs) are key enabling devices for plastic electronics technology, which has a potentially disruptive impact on a variety of application fields, such as health, safety, and communication. Despite the tremendous advancements in understanding the OFET working mechanisms and device performance, further insights into the complex correlation between the nature of the charge-injecting contacts and the electrical characteristics of devices are still necessary. Here, an in-depth study of the metal–organic interfaces that provides a direct correlation to the performance of OFET devices is reported. The combination of synchrotron X-ray spectroscopy, atomic force microscopy, electron microscopy, and theoretical simulations on two selected electron transport organic semiconductors with tailored chemical structures allows us to gain insights into the nature of the injecting contacts. This multiple analysis repeated at the different stages of contact formation provides a clear picture on the synergy between organic/metal interactions, interfacial morphology, and structural organization of the electrode. The simultaneous synchrotron X-ray experiments and electrical measurements of OFETsin operandouncovers how the nature of the charge-injecting contacts has a direct impact on the injection potential of OFETs.